Field of the Invention
The present invention relates to an aqueous ink, an ink cartridge and an ink jet recording method.
Description of the Related Art
In recent years, aqueous inks for ink jet are required to have such characteristics as to enable the recording of high quality images, for example, having high optical density and images having excellent toughness including abrasion resistance and highlighter resistance. Such inks are also required to have excellent reliability including ejection stability and ejection accuracy.
To meet the above requirements, various techniques have been disclosed. For example, in order to record images having high optical density and excellent abrasion resistance, an aqueous ink including what is called a self-dispersible pigment, a water-soluble organic solvent containing a good solvent and a poor solvent for the pigment at a certain ratio and a resin has been disclosed (Japanese Patent Application Laid-Open No. 2006-045514). In addition, an aqueous ink for ink jet including a self-dispersible pigment, a resin and a salt and enabling the recording of images satisfying both the optical density and the toughness (abrasion resistance, highlighter resistance) has been disclosed (Japanese Patent Application Laid-Open No. 2012-214713, Japanese Patent Application Laid-Open No. 2013-253230, Japanese Patent Application Laid-Open No. 2016-044236).
By using the aqueous ink disclosed in Japanese Patent Application Laid-Open No. 2006-045514, Japanese Patent Application Laid-Open No. 2012-214713, Japanese Patent Application Laid-Open No. 2013-253230 or Japanese Patent Application Laid-Open No. 2016-044236, images having high optical density and excellent toughness can be recorded. The result of studies by the present inventors, however, has revealed that irregular ejection may be caused after ejection of such an aqueous ink for a long time with an ink jet recording apparatus, and the irregular ejection is caused more frequently as the number of recording times increases.